The Celestron f/6.3 focal reducer and field flattener is a photographic accessory produces 37% wider fields of view. Exposure times are reduced by a factor of 3.
The resulting f/ratio of f/10 Schmidt-Cassegrains (8", 9.25" and 11" models) with the reducer is f/6.3. The resulting f/ratio when used with 14" Schmidt-Cassegrains is f/7.
The focal reducer threads onto the large 2" threads, in place of the visual back. Schmidt-Cassegrain standard t-adapters thread onto the end of the reducer.
The corrector capabilities help deliver rounder stars towards the edge of the field of view due to field curvature. Field curvature isn't eliminated, but reduced significantly.
Can be used visually, or photographically with DSLR's or film SLR's.